1. Field of the Invention
This invention relates to needleless, gas operated piston-type injectors for introducing predetermined quantities of medicaments interstitially, and especially to such injectors in which a deflagatory pyrotechnic charge provides the fluid-injecting force. More particularly it relates to devices of this type wherein the powering charge, piston and medicament are contained within a disposable ampul.
2. Prior Art
The use of high pressure gas-propelled injectors in lieu of the common hypodermic syringe and needle for subcutaneous injection of fluid medicaments such as vitamins, vaccines, anaesthetics, and the like is well established. A number of typical prior art devices employing this technique are referred to and discussed in U.S. Pat. No. 3,802,430 (Schwebel and Arnold), which teaches the use of a single-shot preloaded pyrotechnic charge or deflagrant to propel a piston-actuated high velocity fluid injection system. In that patented apparatus, as in a number of the other prior art examples of gas operated injectors, both the triggering and actuating mechanisms and the gas-producing means are housed together. With this arrangement once the gas supply is exhausted the entire relatively costly unit, including the triggering and firing mechanisms, is of no further use and must be discarded.
In some instances this problem is obviated by providing for replacement or replenishment of the gas source; however, the structural requirements of this approach tend to make such devices overly complex and expensive to construct and maintain.
The object of the present invention is to provide a needleless, gas operated piston-type injector of sturdy, durable and relatively simple construction which avoids these and other deficiencies associated with the prior art gas operated injectors.